Thermochromic polyacrylamide tissue phantom and its use for evaluation of ablation therapies

ABSTRACT

A polyacrylamide tissue phantom embedded with multi-formulated thermochromic liquid crystals for use in the evaluation of RF ablation therapies is provided. The tissue phantom approximates the properties of biological tissue, and therefore provides a suitable substitute for use in testing the effects of RF and other energy-emitting devices on biological tissue. Also provided is a system for using the tissue phantom in the evaluation of RF therapies.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of patent application Ser. No.13/360,561, filed Jan. 27, 2012, entitled THERMOCHROMIC POLYACRYLAMIDETISSUE PHANTOM AND ITS USE FOR EVALUATION OF ABLATION THERAPIES, theentirety of which is incorporated herein by reference.

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

n/a

FIELD OF THE INVENTION

The present invention relates to a method and system for evaluatingradiofrequency ablation techniques.

BACKGROUND OF THE INVENTION

Ablation therapy, such as radio frequency ablation (RFA), is commonlyused medical procedure in which body tissue is ablated, shrunk, heated,coagulated, or otherwise treated using energy (for example, radiofrequency energy). Common examples of ablation therapies include thetreatment of cardiac arrhythmia, tumor destruction, pain amelioration,and controlling bleeding. Radio frequency ablation devices, for example,may include a power source and/or RF generator, and one or more ablationelements or electrode coupled to the power source.

The efficacy of RFA and other ablation therapies may depend on suchparameters as the type of tissue being treated, the tissue depth towhich the RF energy reaches, and the type and spacing of electrodesused. Also, because ablation typically affects tissue at a depth beneaththe tissue surface, it can be difficult to accurately analyze theoutcome of ablation treatments, including visualization of the ablationpattern and ablation tissue depth. Further, using tissues such asnon-living porcine or cadaver tissues can produce a wide variation inresults because of the non-uniformity of the samples and the subjectiveinterpretation of results. The effectiveness of ablation therapies usingthese methods may only be assessed after cutting, staining, andsubjectively observing the test tissue. All of these factors can maketesting new ablation devices and methods costly and inaccurate. Tissuephantoms provide uniform characteristics and are sometimes used assubstitutes for biological tissue, the properties of which can differsubstantially from sample to sample. For example, heart phantoms may beused for analysis of cardiac motion and freezing properties of cardiactissue; lung phantoms may be used for calibration of medical CTscanners; and entire phantom torsos, including organs, maybe used forlaparoscopic technique training. However, just like biological tissue,it is not always easy to visualize the effects on these tissue phantomsof the medical or testing procedure. Also, many commonly used tissuephantom materials, such as agar, may have a melting point that is lowerthan the testing temperature.

During ablation, in particular RFA, it is important to monitor thetemperature of the electrode to prevent ablation of unintended tissueareas and depths, and to prevent the electrode from overheating. Becausethermochromic materials may provide visualization of minute temperaturegradients, as well as binary threshold temperature confirmation, theyare especially useful in the medical industry. Thermochromic materialsand compounds may be used to indicate when an electrode reaches acertain threshold temperature. For example, binary thermochromicmaterials may be colored and opaque at room temperature, but becometransparent when the threshold temperature is reached. Common uses forthermochromic materials include thermochromic thermometers, batterycharge indicators, and color-change dyes. However, the use ofthermochromic materials has not yet been adapted for use in theevaluation of such medical procedures as RFA.

To accurately evaluate the effectiveness of RFA and other ablationtherapies, it is desired to provide a tissue phantom that could mimic avariety of mammalian tissues and that gives visual confirmation of thetemperature gradient produced within the tissue phantom by theapplication of RF energy. Such a device and method of use would reducevariability in test setup and decrease overall testing time, allowingfor a statistically significant number of tests to be conducted in lesstime than traditional testing methods.

SUMMARY OF THE INVENTION

The present invention advantageously provides a device and method forreliably and consistently measuring the thermal effects of ablationtherapies. In one embodiment, the device may comprise a substancemimicking mammalian body tissue and changing color in response tocontact with an activated ablation device. The substance may be alayered substance, at least one layer being a thermochromic layer. Thelayered substance may further include a substantially transparent secondlayer having a first surface, and a substantially opaque third layerhaving a first surface, the thermochromic layer being between the secondand third layers. Further, the layered substance may be composed atleast in part of polyacrylamide gel, which may be doped with othercompounds, such as salts. The thermochromic layer changes color inresponse to energy such as radiofrequency energy, radiant heat, cooling,microwave energy, or electromagnetic energy. The thermochromic layer mayinclude microencapsulated cholesteric liquid crystals, and may include aplurality of formulations of liquid crystals. Further, each of theplurality of formulations may have a bandwidth of between approximately1° C. and approximately 20° C., and the thermochromic layer may respondto radiofrequency energy over a temperature range of approximately 50°C. to approximately 110° C.

In another embodiment, the device may comprise: a layered polyacrylamidegel mimicking body tissue, including a substantially transparent firstlayer having a first surface and a second surface; a thermochromicsecond layer having a first surface and including thermochromicmicroencapsulated cholesteric crystals that change color in response toablation energy over a temperature range of approximately 50° C. toapproximately 110° C., a substantially opaque third layer having a firstsurface and providing contrast to the second layer, the second layerbeing between the first and third layers; and an energy applicationsurface comprising the first surface of each of the first, second, andthird layers, the width of the thermochromic second layer being betweenapproximately 0.5 mm to approximately 1.5 mm as measured on the energyapplication surface, the width being substantially constant throughoutthe thermochromic second layer. Further, the second and third layers mayeach have a width of between approximately 15 mm and approximately 20 mmas measured on each of the first surfaces of the second and thirdlayers.

The method may comprise providing a substance mimicking mammaliantissue, the substance having a substantially transparent first layerhaving a first surface and a second surface; a thermochromic secondlayer having a first surface and including thermochromic material thatchanges color in response to contact with an activated ablation device,a substantially opaque third layer having a first surface and beingsuitable for providing contrast to the second layer, the second layerbeing between the first and third layers, providing an ablation device;activating the ablation device and placing the device in contact with atleast the first surface of the thermochromic second layer, observingthrough the second surface of the substantially transparent first layerthe color changes in the second thermochromic layer, determining whetherto adjust parameters of the ablation device based on the color changes.The method may further include providing a tank containing a volume ofelectrically conductive fluid, providing a fluid flow chamber in fluidcommunication with the tank and including a pump for circulating thefluid between the tank and the flow chamber, placing the substancewithin the tank so that at least the first surface of the thermochromicsecond layer is submerged within the fluid, providing a camera having atelecentric lens and being positioned in visual communication with thesecond surface of the substantially transparent first layer, placing anactivated ablation device in contact with at least the first surface ofthe thermochromic second layer, and visualizing color changes in thethermochromic second layer through the second surface of thesubstantially transparent first layer using the lens of the camera. Thethermochromic material includes cholesteric liquid crystals, which maybe microencapsulated. The thermochromic material changes color inresponse to at least one of radiofrequency energy, radiant heat,cooling, microwave energy, and electromagnetic energy. Further, thethermochromic material may respond to radio frequency energy over atemperature range of approximately 40° C. to approximately 120° C.Further, the thermochromic material may include a plurality offormulations of liquid crystals, each of formulations having a bandwidthof approximately 20° C. or less.

BRIEF DESCRIPTION OF THE DRAWINGS

A more complete understanding of the present invention, and theattendant advantages and features thereof, will be more readilyunderstood by reference to the following detailed description whenconsidered in conjunction with the accompanying drawings wherein:

FIG. 1A shows a perspective view of an example of a material that mimicsmammalian tissue;

FIG. 1B shows an exploded view of an example of a material that mimicsmammalian tissue;

FIG. 2 shows a schematic view of a testing system;

FIG. 3 shows a close-up cross-sectional image of a thermally affectedlayered thermochromic tissue phantom sample;

FIG. 4 shows cross-sectional images of the layered thermochromic tissuephantom sample, as when evaluating the effects of electrode spacing onlesion development; and

FIG. 5 shows a chart of cross-sectional images of both porcine tissueand layered thermochromic tissue phantom to compare lesion developmentin both tissues over time.

DETAILED DESCRIPTION OF THE INVENTION

The present invention advantageously provides a method and system forreliably and consistently measuring the thermal effects of ablationtherapies, and may be used to evaluate effectiveness of various ablationdevices.

As used herein, reference to the tissue phantom “mimicking mammaliantissue” means that the tissue phantom has one or more properties thatare substantially consistent with living mammalian tissue. Suchproperties may include thermal conductivity, electrical conductivity,pH, texture, water content, and others.

As used herein, any reference to ablation, ablation technology, orablation device, may include any type of same, unless otherwisespecified. Such ablation technologies may include radiofrequencyablation, cryoablation, ultrasound ablation, laser ablation, or others.An ablation device as used herein may be any device that is capable ofemitting energy (such as an RFA catheter) or absorbing energy (such as acryoablation catheter). Likewise, an “energy generator” as used hereinmay be a device that creates energy (such as an RF generator) orprovides for the removal of energy (such as a Peltier cooler orthermoelectric cooler). Accordingly, reference to “applying energy”herein may also be interpreted to include the removal of energy.

Referring now to FIGS. 1A and 1B, a perspective view and an explodedview of an example of a material that mimics mammalian tissue are shown.The material may be a layered thermochromic tissue phantom 10 thatchanges color when in contact with an activated ablation device. Thelayered thermochromic tissue phantom 10, generally referred to herein as“tissue phantom,” may be composed of polyacrylamide or other substancehaving substantially similar characteristics, although the tissuephantom 10 may also include other ingredients. The tissue phantom 10 maybe in a substantially gel state (that is, the tissue phantom 10 is solidenough to hold a desired shape). Polyacrylamide gel (PAG) is well suitedfor use in evaluating ablation therapies and devices because the PAG maybe doped with a salt to mimic the electrical conductivity of varioushuman tissues, for example, NaCL or KCl. Additionally, PAG has a meltingpoint that is higher than the temperature range optimal for testingablation therapies, both at the surface and below the surface of the PAG(subsurface temperatures may be higher than the surface temperature).The tissue phantom 10 may include a plurality of polyacrylamide layers,depending on the one or more compounds added to a particular layer. Forexample, as shown in FIG. 1, the tissue phantom 10 includes threelayers. The first layer 12 may be composed essentially of substantiallytransparent polyacrylamide, the second layer 14 may be composedessentially of polyacrylamide embedded with a thermochromic materialthat changes color in response to the application of energy (such as RFenergy), and the third layer 16 may be substantially opaque and composedessentially of polyacrylamide and dye. Each layer 12, 14, 16 has a firstsurface 12 a, 14 a, 16 a, respectively, the first surfaces 12 a, 14 a,16 a together comprising an energy application surface 17 (however, thiscould also be the surface from which energy is removed, such as whentesting cryoablation devices). Widths and depths of the layers 12, 14,16 are determined as depicted by the bracketed areas in FIG. 1B.

In order to test an ablation device, the electrodes of the device areplaced on the energy application surface 17. The electrodes are placedin contact with at least the first surface 14 a of the second layer 14,but may also be placed in contact with the first surfaces 12 a, 16 a ofthe first 12 and third 16 layers. The thermal effects of the activatedablation device may be observed in the second layer 14. Color changes inthe thermochromic second layer 14 are not permanent, and so the tissuephantom 10 may be used for multiple tests.

Continuing to refer to FIGS. 1A and 1B, the first layer 12 of clearpolyacrylamide is referred to as the “visualization layer” because itmay be possible to see the thermochromic second layer 14 through thisfirst layer 12. In one non-limiting embodiment, the first surface 12 aof the visualization layer 12 is between approximately 15 mm andapproximately 20 mm wide, as measured at the first surface 12 a.However, the visualization layer 12 may have any width that permitsundistorted viewing therethrough of the second layer 14. Thevisualization layer 12 may also have a second surface 12 b through whichthe thermochromic second layer 14 may be visible.

Continuing to refer to FIGS. 1A and 1B, the second layer 14 ofpolyacrylamide embedded with thermochromic material is referred to asthe “TLC” layer. In one non-limiting embodiment, the TLC layer 14 isbetween approximately 0.5 mm and approximately 1.5 mm as measured on thefirst surface 14 a, the width being substantially constant throughoutthe layer. For example, the layer may have a standard deviation of ±0.5mm. Within this width range, the TLC layer 14 may be thick enough tohold an amount of thermochromic liquid crystals sufficient for testingpurposes, but also be thin enough to precisely visualize color changes.

The thermochromic material may be water-miscible, microencapsulatedthermochromic liquid crystals (referred to herein as “TLC compound”),such as cholesteric crystals (for example, cyanobiphenyls andcholesteryl nonanoate), chiral nematic crystals, or combination thereof.Although the mechanism by which all of these thermochromic liquidcrystals change color may be the same, cholestric and chiral nematicformulations may have different chemical and physical characteristics.For simplicity, however, all are collectively referred to with thegenerally accepted nomenclature of “cholesteric liquid crystals.” TheTLC compound includes one or more thermochromic formulations, the numberand characteristics of the formulations depending on the desiredtemperature range to be represented in color gradients. As shown anddescribed in FIG. 4, these gradients substantially correspond to thedimension of a lesion created in biological tissue. Based on thesevisual effects, a user may adjust such features of the ablation deviceas number, size, distribution, and type of electrodes used.

Continuing to refer to FIGS. 1A and 1B, the third layer 16 ofpolyacrylamide and dye is referred to as the “contrast layer.” The dyemay be a dark-colored dye, such as a black dye (for example, BrilliantBlack dye), in order to enhance the colors of the TLC layer 14 whenviewed through the visualization layer (that is, provide contrast to theTLC layer 14). The dye should be water-miscible, and should not be addedin a concentration that would result in leeching into or otherwiseaffecting or distorting the TLC layer 14. In one non-limitingembodiment, the contrast layer 16 is between approximately 15 mm andapproximately 20 mm wide, as measured at the first surface 16 a.However, the contrast layer 16 may have any width that provides anadequate background for visualization of the TLC layer 14.

An ablation device is applied to the tissue phantom 10, with the one ormore electrodes at least in contact with the first surface 14 a of theTLC layer 14, although the electrodes may also be in contact with thefirst surfaces 12 a, 16 a of the visualization layer 12 and contrastlayer 16 as well. When placed in contact with the tissue phantom 10, theactivated ablation device may have no perceivable effect on thevisualization and contrast layers 12, 16; however, contact with theactivated ablation device will produce colored gradients within the TLClayer 14 that correspond to the temperature of the TLC layer within thetemperature range of the TLC compound. For example, as shown anddescribed in FIG. 3, the TLC compound may be formulated to respond toradiofrequency energy over a temperature range of approximately −30° C.to approximately 120° C., although a temperature range of approximately40° C. to approximately 120° C. may be used when testing such ablationtherapies such as RF ablation.

In a non-limiting example, four different thermochromic crystalformulations may be combined in the TLC compound. A first formulationmay have a red start (the temperature at which a clear PAG will turn ared color) at approximately 50° C. and a bandwidth of approximately 2°C. This means that this formulation may cause thermally affected areasof the TLC layer 14 to turn red at approximately 50° C., to turnmid-green at approximately 51° C., and to turn blue at approximately 52°C. (an overall 2° C. bandwidth). The blue color will persist until aclearing temperature is reached and the PAG turns clear. At thisclearing point, a second formulation may begin showing color. Forexample, a second formulation may have a red start at approximately 60°C. and a bandwidth of approximately 2° C., a third formulation may havea red start at approximately 70° C. and a bandwidth of approximately 2°C., and a fourth formulation may have a red start at approximately 80°C. and a bandwidth of approximately 2° C. The thermochromic crystals ineach formulation may appear colorless below and above the appropriatebandwidth temperatures, only displaying color when the temperature iswithin the bandwidth for the formulation. Thus, in this example, the TLClayer 14 displays color representation over a temperature range ofapproximately 50° C. to approximately 82° C. (through the anisotropicchiral or twisted nematic phase), and appears colorless belowapproximately 50° C. (crystallic phase) and above approximately 82° C.(isotropic phase/clearing point). This temperature range is appropriatefor evaluating most ablation therapies and devices because a chroniclesion (that is, tissue ablation) may occur at approximately 50° C. andabove, such as when using RF ablation. Further, using formulations witha small bandwidth (for example, 2° C. as compared to a bandwidth of 20°C.) makes the color bands narrower, so a single band can be isolatedfrom which to draw data points instead of judging temperature based onhue in wider color bands resulting from a formulation having a largerbandwidth. However, formulations may be provided that display colorrepresentation over a temperature range of approximately −30° C. toapproximately 120° C.

It should be noted that the overall polyacrylamide formulation used inall layers of the tissue phantom 10 may be adjusted to mimic a varietyof test tissues. For example, the PAG may be doped with various amountsa salt such as NaCl to mimic the electrical conductivity of differentmammalian tissues. Additionally, the PAG may be doped with othercompounds to adjust such parameters as the thermal conductivity, pH, andmoisture content of the tissue phantom 10. For example, glycerol may beadded to the PAG to adjust thermal properties of the tissue phantom 10.The tissue phantom 10 may also be molded to resemble any shape,including human internal organs. No matter what the shape of the tissuephantom 10, however, the tissue phantom 10 may still include avisualization layer 12, a TLC layer 14, and a contrast layer 16.Further, the TLC layer may be between 0.5 mm and 1.5 mm wide, asmeasured at the first surface 14 a, the width being substantiallyconstant throughout the layer. Further, a substantially flat (planar)TLC layer 14 may enhance viewability of the color representation within.Further, for irregular tissue phantom 10 shapes, the visualization 12and contrast 16 layers may each have a depth that is greater or lessthan the TLC layer 14; however, the depths of the visualization 12 andcontrast 16 layers may be at least equal to the active area of the TLClayer 14 (that is, the area over which color representation isdisplayed).

Referring now to FIG. 2, a schematic view of a testing system 20 isshown. In one embodiment, the testing system includes a tissue phantom10, an ablation device 22 and energy generator 24 (such as an RFgenerator) for the application of energy to the tissue phantom 10, acamera 26 for imaging color gradients in the tissue phantom 10, a tank28 for containing saline or other electrically conductive fluid, adevice holder 29 for holding the ablation device 22 in position, a flowchamber 30 for generating and adjusting the flow of electricallyconductive fluid through the tank 28, and a flow nozzle 31 in fluidcommunication with the flow chamber 30 and tank 28.

Continuing to refer to FIG. 2, the ablation device 22 (such as an RFablation device) and energy source 24 (such as an RF generator) may beused to apply (or remove) energy to the tissue phantom 10. Accordingly,the TLC layer 14 compound may be adjusted as necessary to produce colorrepresentation in the relevant temperature range. The ablation device 22may be stabilized and held within a device holder 29 positioned abovethe tissue phantom 10, which may be either integrated with a part of thesystem (for example, affixed to the tank 28) or be a free-standing frameor device. In one embodiment, a multi-array ablation catheter (forexample, Ablation Frontiers MAAC® Multi-Array Ablation Catheter®) and RFgenerator (for example, Ablation Frontiers GENius™ Multi-Channel RFGenerator) are used. The device 22 may include one or more electrodes32, which may be composed of platinum or other electrically conductivemetal. The generator 24 may include one or more energy modes (forexample, bipolar, unipolar, 4:1, 2:1, and 1:1 modes of an RF generator).During testing, parameters such as electrode 32 number and spacing andgenerator 24 modes may be adjusted and resulting effects on the TLClayer 14 of the tissue phantom 10 evaluated.

Continuing to refer to FIG. 2, a camera 26 may be used to image colorgradients within the TLC layer 14 of the tissue phantom 10. The camera26 may be affixed to the tank 28 or otherwise positioned for anunimpeded view of the tissue phantom 10 within the tank 28 (in visualcommunication with the second surface 12 b of the visualization layer12). The camera 26 may be, for example, a CCD or CMOS camera, may havean internal or external power source, and may be in electricalcommunication with a computer or other data storage device.Additionally, the camera 26 may be capable of producing still images,video images, or both. Alternatively, a lens (simple lens or compoundlens) or the naked eye may be used to image the color representation inthe tissue phantom 10. In one embodiment, a video camera having atelecentric lens is used, as shown in FIG. 2. A video of the tissuephantom 10 as energy is applied may be taken by the camera 26, in orderto evaluate the change in temperature of the tissue phantom 10 overtime. Or, the camera 26 may take a series of still images (for example,at the rate of one frame per second), which can be used to evaluatecolor representation over time.

Continuing to refer to FIG. 2, a tank 28 and flow chamber 30 may be usedto contain and control the flow of an electrically conductive fluid,such as saline. The tissue phantom 10 may be placed within the tank 28so that at least the first surface 14 a of the TLC layer 14 may be incontact with the electrically conductive fluid. The flow chamber 30 maybe in fluid communication with the tank 28 and may include a pump inconnection with a power source for circulating the fluid within the tank28 and between the tank 28 and the flow chamber 30. For example, theelectrically conductive fluid may flow from the flow chamber 30 to thetank 28 through a flow nozzle 31 that applies an adjustable stream offluid over the ablation surface 17 of the tissue phantom 10. Theelectrically conductive fluid, and flow thereof, may be a variable thatis adjusted for evaluating the effects of energy emission (such as RFenergy emission) on the tissue phantom 10. Additionally, the flow rateof the fluid may affect the power and temperature of the device 22 beingtested. This effect may be useful when testing device 22 technology, forexample, when testing the efficiencies of various RFA electrodes.Alternatively, however, an electrically conductive fluid may not beused, and instead the results of the therapy on the tissue phantom 10may be evaluated without accounting for the effects of the fluid.

Continuing to refer to FIG. 2, the system 20 may further include one ormore glare shields 34 for reducing glare from the electrodes that mayhinder visualization of the color representation in the TLC layer 14.Further, the system 20 may include a dark contrast backdrop (againstwhich the entire tissue phantom 10 may be viewed), one or more lightsources, frames, clamps, hoses, conduits, connectors, valves, powersources, displays, computers, user input devices, user control devices,and other components for efficient device 22 testing and system 20operation. Further, the system 20 may be operable by or in cooperationwith automated capture and analysis software.

Referring now to FIG. 3, a close-up cross-sectional image of a thermallyaffected layered thermochromic tissue phantom sample is shown. As shownand described in FIG. 1, the TLC compound displays colors correspondingto a range of temperatures (color representation), for example, fromapproximately 50° C. to approximately 100° C. As a non-limiting example,an RFA device 22 such as an Ablation Frontiers MAAC® Multi-ArrayAblation Catheter® may be used with an Ablation Frontiers GENius™Multi-Channel RF Generator 24. As shown and described in FIG. 4, thecolor representation of FIG. 3 substantially corresponds to thedimensions of an RFA lesion created in biological (mammalian) tissue. Acomputer program or mathematical formula may be used to interpolatetemperature between bands of the color representation and to extrapolatetemperature beyond the temperature range within each color band based onthe one or more TLC formulations used in the TLC layer 14. Areas of theTLC layer 14 that are at a temperature above or below the temperaturerange of the one or more combined TLC formulations appear transparent oruncolored.

Referring now to FIG. 4, cross-sectional images of the layeredthermochromic tissue phantom sample 10, as when evaluating the effectsof electrode 32 spacing on lesion development, are shown. FIG. 4 is anon-limiting example of the type of ablation device data that can begathered using a tissue phantom 10. The term “set point” refers to thetemperature to which at least a portion of the device 22 is brought. Forexample, a 55° C. set point means that the electrodes 32 of an ablationdevice 22 are brought to and maintained at a temperature of 55° C. Then,the thermal effects on the tissue phantom 10 at this electrodetemperature setting may be evaluated by visualizing color representationin the TLC layer 14. Because the color representation corresponds to alesion created in mammalian tissue, a user can easily and accuratelyevaluate subsurface effects of a device 22 when operated at various setpoints. Based on these visual effects, a user may adjust the device 22by, for example, adjusting the spacing between electrodes 32.

Referring now to FIG. 5, a chart of cross-sectional images of bothporcine tissue and layered thermochromic tissue phantom to comparelesion development in both tissues over time are shown. This series ofimages illustrates the suitability of the tissue phantom 10 as areplacement for mammalian tissue during testing. That is, the series ofimages shows that the areas of TLC layer 14 in the tissue phantom 10very closely correspond to the lesions created in biological tissueusing the same energy application method. In the first (lefthand) columnof the chart, the time course over which energy is applied is shown. Forthis series of images, an RF generator set to 4:1 energy mode is used.In the second and third columns, the thermal affects of energyapplication on both mammalian tissue (for example, porcine thigh muscletissue) and the tissue phantom 10 is shown, respectively. For example,RF energy may be applied to both mammalian tissue and the tissue phantom10 over a course of two minutes, with the effects on both tissues beingcompared at 15-second or 30-second intervals. The 45- and 60-secondinterval images each include a faint transition zone corresponding to anisotherm line: a 50° C. isotherm line is shown in the 45-second intervalimages of mammalian tissue and tissue phantom, and a 60° C. isothermline is shown in the 60-second interval images of mammalian tissue andtissue phantom. These lines demonstrate the correlation between colorrepresentation of temperature in the TLC layer 14 of the tissue phantom10 and the lesion created in mammalian tissue. In FIG. 4, an RFA deviceand RF generator set to 4:1 mode are used for the treatment of bothtissues. For each time interval in FIG. 4, the mammalian tissue wasfirst cut and stained with 2,3,5-Triphenyltetrazolium chloride (TTC)before an image was taken of the lesion. In contrast, the colorrepresentation in the TLC layer 14 of the tissue phantom 10 was easilyimaged in real-time without the need for cutting, staining, or otherwisealtering the tissue phantom 10.

It will be appreciated by persons skilled in the art that the presentinvention is not limited to what has been particularly shown anddescribed herein above. In addition, unless mention was made above tothe contrary, it should be noted that all of the accompanying drawingsare not to scale. A variety of modifications and variations are possiblein light of the above teachings without departing from the scope andspirit of the invention, which is limited only by the following claims.

What is claimed is:
 1. A device for visualizing thermal treatmentpatterns, the device comprising: a first layer having a first surface; asecond layer having a first surface; a third layer having a firstsurface, the second layer being between the first and third layers, thefirst surface of the first layer, the first surface of the second layer,and the first surface of the third layer together defining an energyapplication surface, at least a portion of the energy applicationsurface being substantially transparent, at least a portion of theenergy application surface changing colors in response to theapplication of energy to the energy application surface, and at least aportion of the energy application surface being substantially opaque. 2.The device of claim 1, wherein the first layer is substantiallytransparent, the second layer is thermochromic and changes colors inresponse to the application of energy to the energy application surface,the second layer being visible through the substantially transparentfirst layer, and the third layer being substantially opaque andproviding contrast to the thermochromic second layer.
 3. The device ofclaim 1, wherein the device is composed at least in part ofpolyacrylamide gel.
 4. The device of claim 3, wherein the polyacrylamidegel is doped with at least one of a salt and glycerol.
 5. The device ofclaim 1, wherein the second layer has a substantially constant widthbetween approximately 0.5 mm and approximately 1.5 mm as measured on thefirst surface of the second layer.
 6. The device of claim 2, wherein thethermochromic second layer changes color in response to at least one ofradiofrequency energy, radiant heat, cooling, microwave energy, andelectromagnetic energy.
 7. The device of claim 2, wherein thethermochromic second layer includes at least one of microencapsulatedcholesteric liquid crystals and microencapsulated chiral nematic liquidcrystals.
 8. The device of claim 7, wherein the thermochromic secondlayer includes a plurality of formulations of liquid crystals, with eachof the plurality of formulations having a bandwidth of approximately 2°C.
 9. The device of claim 2, wherein the thermochromic second layerresponds to radiofrequency energy over a temperature range of betweenapproximately −30° C. and approximately 120° C.
 10. A method ofevaluating thermal treatment patterns, the method comprising: contactingan activated ablation device with a tissue phantom, the tissue phantomincluding: a substantially transparent first layer having a firstsurface; a thermochromic second layer having a first surface andincluding thermochromic material that changes color in response tocontact with the activated ablation device; and a substantially opaquethird layer having a first surface, the second layer being between thefirst and third layers, the first surface of the substantiallytransparent first layer, the first surface of the thermochromic secondlayer, and the first surface of the substantially opaque third layertogether comprising an energy application surface with which theactivated ablation device is placed in contact; and determining whetherto adjust parameters of the ablation device based on the color changesin the thermochromic second layer.
 11. The method of claim 10, whereinthe color changes in the thermochromic second layer are visible throughthe substantially transparent first layer.
 12. The method of claim 11,wherein the substantially opaque third layer provides contrast to thethermochromic second layer.
 13. The method of claim 10, furtheringincluding: placing the tissue phantom within a tank containing a volumeof electrically conductive fluid such that at least the first surface ofthe thermochromic second layer is submerged within the fluid, the tankbeing in fluid communication with a fluid flow chamber and a pump thatcirculates the electrically conductive fluid between the tank and theflow chamber; and contacting an activated ablation device with theenergy application surface.
 14. The method of claim 13, wherein thesubstantially transparent first layer includes a second surface, themethod further including: providing a camera having a telecentric lens,the camera being positioned in visual communication with the secondsurface of the substantially transparent first layer; and visualizingcolor changes in the thermochromic second layer through the secondsurface of the substantially transparent first layer using the lens ofthe camera.
 15. The method of claim 10, wherein the thermochromicmaterial includes microencapsulated cholesteric liquid crystals.
 16. Themethod of claim 15, wherein the thermochromic material changes color inresponse to at least one of the group consisting of radiofrequencyenergy, radiant heat, cooling, microwave energy, and electromagneticenergy.
 17. The method of claim 10, wherein the thermochromic secondlayer has a substantially constant width of between approximately 0.5 mmand approximately 1.5 mm as measured on the first surface.
 18. Themethod of claim 10, wherein the thermochromic material responds toradiofrequency energy over a temperature range of between approximately40° C. and approximately 120° C.
 19. The method of claim 18, wherein thethermochromic material includes a plurality of formulations of liquidcrystals, each of formulations having a bandwidth of approximately 20°C. or less.
 20. The method of claim 10, wherein the tissue phantom iscomposed at least partially of polyacrylamide gel doped with at leastone of a salt and glycerol.
 21. The method of claim 10, wherein theparameters of the ablation device include spacing between electrodes.22. A method of evaluating thermal treatment patterns, the methodcomprising: contacting an activated thermal treatment device with atissue phantom, the tissue phantom including: a substantiallytransparent first layer having a first surface and a second surface; athermochromic second layer having a first surface and includingthermochromic material that changes color in response to the contactwith the activated thermal treatment device; and a substantially opaquethird layer having a first surface, the second layer being between thefirst and third layers, the first surface of the substantiallytransparent first layer, the first surface of the thermochromic secondlayer, and the first surface of the substantially opaque third layertogether defining an energy application surface with which the activatedthermal treatment device is placed in contact, color changes within thesecond layer being visible through the second surface of thesubstantially transparent first layer and the substantially opaque thirdlayer providing contrast to the thermochromic second layer, the tissuephantom being submerged within a tank containing a volume ofelectrically conductive fluid; and determining whether to adjustparameters of the ablation device based on the color changes in thethermochromic second layer observed through the second surface of thesubstantially transparent first layer.